/Engine/Source/Runtime/Slate/Public/Widgets/SViewport.h
Called when a touchpad touch is started (finger down)
virtual [FReply](API\Runtime\SlateCore\Input\FReply) OnTouchStarted ( const [FGeometry](API\Runtime\SlateCore\Layout\FGeometry) & MyGeometry, const [FPointerEvent](API\Runtime\SlateCore\Input\FPointerEvent) & InTouchEvent )